Compression pad



J. A. MARGEDANT GOMPRESS ION PAD Feb. 15, 1966 2 Sheets-Sheet 1 Filed NOV. 21, 1962 jam/7- United States Patent Oflice 3,234,774 Patented Feb. 15, 1966 3,234,774 COMPRESSION PAD James A. Margedant, Bloomfield, Mich., assignor to E. I. du Pont de Nemours and Company, Wilmington, Del., a corporation of Delaware Filed Nov. 21, 1962, Ser. No. 239,181 3 Claims. (Cl. 72-294) This invention relates to an improved apparatus for performing working operations, such as trimming, piercing, or flanging, on sheet metal shapes often obtained from a previous draw die operation and to a die member composed of certain cured polyalkyleneether polyurethanes for use in said apparatus.

When metal is stamped out in a press, a flashing or feather edge is left around the edge of the stamped out piece. This edge has to be removed by a separate die often referred to as a trim die. In the conventional trim die, one of the die members is backed-up by a heavy spring. This die member, or compression pad, is usually made of metal and the face thereof often has the configuration of the stamped out metal part. Depending on the shape of the metal part, the forming of the face of the compression pad can be a very expensive operation involving accurate machining. The same is true for compression pads used in dies for piercing, flanging and the like. In the foregoing working operations, the compression pad does no forming, but serves to position the metal part particularly in the region where the trimming, piercing, fianging, etc. is to occur so as to prevent undesirable burring or bulging of the metal part. Consequently, properties such as high impact strength and dimensional stability under load are required of the compression pad. It would be desirable to be able to obtain a compression pad from a material that can be cast into the shape required so as to avoid expensive machining and yet has suflicient strength properties so as to' be useful in a practical sense in such an application as trimming and the like.

It is an object of the present invention to provide a die apparatus which employs a compression pad made of an elastomeric material which does not require expensive machining. It is a further object to provide a compression pad made of certain cured polyalkyleneether polyurethanes which possess a combination of physical properties that make the use of these materials in a compression pad both practical and successful. It is a particular object of this invention to provide a compression pad for use in positioning a stamped metal part during subsequent working operations, which pad can be cast into the shape of a face of the metal part and which possesses high impact strength, hardness, and dimensional stability under loaded conditions and yet has a degree of estensibility to prevent fracturing due to brittleness. These and other objects will appear hereinafter.

These and other objects are accomplished in a die apparatus for performing working operations on a prior substantially formed metal part and having opposing die members, the faces thereof being shaped generally complementary to each other and to corresponding faces of the metal part, the improvement comprising having one of the die members, namely the compression pad, consisting essentially of an elastomeric polyalkyleneether polyurethane composition having a modulus at 100% elongation of 1500 to 4500 lb./sq. in., elongation at the break of 200 to 500%, a Shore D hardness of 45 to 80, and an Izod notch impact minimum of foot lb./in of notch. The polyurethane composition can contain metal particles as filler, in which case these properties will be modified as desired for the requirements of any particular application.

The polyurethane composition can be further defined as being a cured isocyanato terminated prepolymer. This prepolymer results from the reaction between (a) a molar proportion of polytetra-methyleneether glycol having a molecular weight of about 1000, ('b) 0 to 1 molar proportion of 1,3-butanediol, and (c) 2 to 4 molar proportions of toluene diisocyanate, the ratio of -NCO groups of the diisocyan-ate to -OH groups of the glycol and the diol being about 2. The prepolymer is then cured to an elastomeric form in the compression pad shape desired having the above described properties by reaction with to 99% of theory of para,para'-methylene bis(orthochloroaniline), i.e., sufficient -NH groups to react with 85 to 99% of the -NCO groups present.

The present invention will be better understood by reference to the drawings which depict several representative embodiments, but by no means all, of the manner in which a die member, i.e., a compression pad made of a cured polyalkyleneether polyurethane having the foregoing mentioned properties can be used and in which:

FIG. 1 shows in cross section a side elevation of a simplified version of a trim and pierce die arrangement in the open position and containing a compression pad according to the present invention;

FIG. 2 shows the die set of FIG. 1 in the closed position; and

FIG. 3 shows in cross section a side elevation of a simplified version of a flange die arrangement in the closed position and containing a compression pad according to the present invention.

With reference to FIG. 1, a simplified version of a die set 40 is shown consisting of an upper die shoe 1 and lower die shoe 2 installed in a press (not shown) by conventional means. Lower die member 3 is mounted on lower die shoe 2 and the upper die member 4 which in this embodiment is the compression pad 4 of the present invention is mounted slidably within downwardly extending flange portions 5 and 6 of the upper die shoe '1. Compression springs 7 are contained between shoe 1 and compression pad 4 by corresponding depressions -8 in the shoe and the pad. The opposing faces of the compression pad 4 and the lower die member 3 are complementary to each other and to the configuration of the formed sheet 9 placed upon the lower die member. For illustrative purposes, the formed sheet 9 is arcuately shaped and both trimming and piercing thereof is necessary.

For piercing, punches 10 are mounted in a downwardly extending position from upper die shoe 1. Compression pad 4 has corresponding apertures 11 to accommodate punches 10. In the region of apertures 11 are positioned inserts 12 which are composed of a polyurethane type material similar to the composition of the compression pad. The use of inserts such as 12 in the region of piercing of the sheet 9 is preferred since in case of wear in the region of apertures 11 or in case of some relocation of the holes in sheet 9, for design reasons, the pad 4 can be repaired or modified to be used further. In the lower die member 3, cutting-type steel inserts 13 are positioned with apertures 14 in line with punches 10. Both inserts 12 and 13 have faces which are continuations of the opposing faces of their respective die members 3 and 4.

For trimming of two sides of sheet 9, cutting tools 15 are mounted upon flanges 5 and 6 of upper die shoe 1 and cutting tools 16 are mounted in lower die members 3. Cutting tools 15 and 16 are spaced so that when the die set 40, i.e., shoes 1 and 2, is closed as in FIG. 2, sheet 9 is tightly positioned between compression pad 4 and lower die member '3 by action of compression springs 7, and the tools 15 and 16 mate to shear sheet 9, thus cleanly removing scrap portions 17 therefrom. Sheet 9 is also pierced by punches 10 during the closing of the ticles or aluminum particles or metal fibers.

die .set. The punched-out portions of sheet 9 are led away from the piercing zone by channels 18 in the lower die member 3.

In FIG. 3, the cutting tools and 16 of FIGS. 1 and 2 are replaced by similar tools 19 and 20, respec tively, which upon closing of the die set 40, form a flange at two ends of sheet 9. Of course, the width of the lower die member 3 and thus the distance between the tools 20 mounted thereon is less than the distance between the tools 19 by an amount readily determinable by those skilled in the particular art and depending on such factors as the degree of bending desired, sheet 9 thickness, etc.

The stripper pads for trim and pierce dies and flange pads for flange dies, said pads being generally characterized as compression pads, may be molded in a wide variety of shapes depending entirely on the nature of the die for which it is used. The compression pad may be cast in a mold in one uniform pour or the mold may be partitioned so that different parts of the pad are made from different polyurethane compositions. When this is done, it is usually desirable to permit the initial pour to become solid before the second or subsequent formulations are added. Also separately cast pieces may be assembled to form a single pad.

It is frequently desirable to fill the polyurethane with metal particles. It is convenient to use commercially available finely divided metal such as crushed steel par- The metal particles should be in the form of a relatively fine powder, preferably of a size which will pass through a 100-mesh screen (United States Bureau of Standards, Standard Screen Series) depending upon the particular application. From about 200 to 600 parts by weight of metal powder and as much as 800 parts by weight thereof may be added to 100 parts of polyurethane. The method of incorporation will be described later.

The polyalkyleneether polyurethane is prepared from a polytetramethyleneet'her glycol of molecular weight approximately 1000 to which may be added up to an equal molar amount of 1,3-butanediol. It is necessary to use this particular polytetramethyleneether glycol in order to achieve the desired balance of strength and elasticity. An important characteristic of the compression pad composition is a relatively high modulus. In this particular instance, we mean the load which is necessary to produce 100% elongation. The addition of 1,3-butanediol to the polytetramethyleneether glycol has the effect of giving an increased modulus to the cured polyurethane. The molecular weight of the polytetramethyleneether glycol may vary somewhat from 1000, but, in general, should lie between 900 and 1100.

To the polytetramethyleneether glycol or its mixture with 1,3-butanediol is added toluene diisocyanate in the ratio of 2 moles of the diisocyanate for each mole of glycol or the sum of polytetramethyleneether glycol and 1,3-butanediol. The addition is usually made at room temperature under anhydrous conditions and with agitation. The mass is then heated to about 80 C. for about .4 hours. There results an isocyanate-terrninated prepolymer which, depending upon the proportion of butanediol incorporated, will contain from about 6% to about 9.5% free -NCO groups. Toluene-2,4-diisocyanate is used in preparing these compositions, however, as much as 20% of the toluene-2,6-diisocyanate isomer may be present. It has been found if the molar ratio of diisocyanate to glycol is substantially lower or substantially higher than 2: 1, the resulting polyurethane does not have the properties that are required to make compression pads. If the ratio is less than 2:1, the prepolymer has a higher average molecular weight and there is a corresponding lower percentage of free NCO groups and thus there is a greater distance between the urea groups formed when the isocyanate-terminated prepolymer is reacted with a diamine curing agent.

The isocyanate-terminated prepolymer is mixed with a curing agent immediately before casting it into the compression pad mold. The pot-life of the mixture is relatively short. The prepolymer and the curing agent may be mixed either batchwise or continuously. In either case, the preferred curing agent, para,paramethylene bis(ortho-chloroaniline), is melted first at a temperature of 120 C. and added to the prepolymer which is at 70 C., with very efficient mixing. Since the pot-life is on the order of 1 to 5 minutes, it is preferable to use a continuous mixing device when large castings are to be made.

The polyurethane thus formed is then let stand to harden at about 50 C. for about 50 hours. At higher temperatures final curing of the polyurethane takes place more rapidly. At lower temperatures, longer times are required. Shrinkage which is always a problem in castings, is minimized at the lower curing temperatures.

When finely ground metal particles are added, they are put into the mix immediately after the diamine has been added. The metal particles should be dry and free from contamination. If they are not, there can be a problem in the adhesion of the polyurethane to the metal particles.

It has been found that either metal filled or plain polyurethane compression pads must have certain physical characteristics to stand the mechanical action inherent in their use. Surprisingly, it has been found that the particular combination of glycols and diisocyanates with this particular diamine give a composition which will withstand this action. For example, it has been found that one such compression pad was still in good condition after over 100,000 cycles. Under similar conditions, epoxy resin compositions which have been used for this purpose will fail at 20,000 to 30,000 cycles and frequently fewer.

The physical properties which are given previously are the properties of the polyurethane per se. When the polyurethane is filled with crushed metal, these properties are obviously different. For instance, the Izod impact strength is lower than the minimum of 10 foot lb./sq. in. previously specified. However, the value should not drop below 1. By the same token, the other values will be different depending on the amount of metal filler which is put into the polyurethane composition.

The tests on the unfilled polyurethanes are made according to the following standard methods.

ASTM D 412-611" Modulus, tensile, elongation.

ASTM D 148459 Shore D hardness.

ASTM D 25656 Impact resistance, Izod.

ASTM D 39561 Compression set (Method Instron Method B Compressiondeflection,

shape factor 0.375.

The following examples, in which parts are by weight unless otherwise indicated, are representative of the present invention which is not limited therein except as defined in the appended claims.

EXAMPLE 1 To 250 parts of polytetramethyleneether glycol 1000 (molecular weight) and 22.5 parts of 1,3-butanediol at 30 C. there is added 174 parts of a :20 mixture of toluene2,4- and 2,6-diisocyanate. The mixture is then heated to 80 C. for 4 hours. After cooling at room temperature, analysis showed 9.26% NCO groups.

parts of this prepolymer is then heated to 70 C. and 26 parts of molten para,para'-methylene bis(ortho chloroaniline) at C. were added. After thoroughly mixing for about 30 seconds the mass is poured into a mold for a compression pad for a door panel, which is then heated for 1 hour at 100 C. After standing for 1 week at room temperature and 50% relative humidity, it had the following properties:

Two master-batches of polyurethane prepolymer are made up by the procedure of Example 1 using the following proportions:

Prepolymer A 1.0 mol polytetramethyleneether glycol, molecular weight 2.0 mol toluene-2,4-diisocyanate Prepolymer B 1.0 mol polytetramethyleneether glycol, molecular weight 1.0 mol 1,3-butanediol 4.0 mol 80% toluene-2,4-diisocyanate/20% toluene-2,6-

diisocyanate Prepolymer A has an -NCO content of 6.45% and Prepolymer B has an --NCO content of 9.4%

These prepolymers are blended (parts by weight) as shown in the following table, heated to 70 C. and the quantity of molten para,para-methylene bis(ortho-chloroaniline) shown is added. After mixing thoroughly, the masses are poured into vent shroud compression pad molds and heated for 1 hour at 100 C. After standing for one week at room temperature at 50% relative humidity the polyurethanes have the properties shown in the table.

Number 1 2 3 4 5 Prepolymer B 100 75 50 25 Prepolymer A 25 50 75 100 p,p-methylene bis(ochloroaniline) 26 27 24. 5 22 19. 5 Modulus at 100% elongation, lbJsq. in 4, 300 3, 850 3, 050 2, 375 2, 100 Tensile strength at break,

./sq. in 10, 000 8, 800 8, 850 8, 400 8, 000

Elongation at break, percent 260 285 290 315 450 Shore D hardness 73 71 G8 60 52 Izod impact resistance,

notched, it. lb./in. notch 15 20+ 20+ flexed flexed Compression set (Method A, 22 hrs. at 70 0., 1350 p.s.i. load), percent 7 5 7 13 EXAMPLE 3 700 parts of polytetramethyleneether glycol 1000 is put into a dry vessel with an agitator. To this is added 244 parts of toluene-2,4-diisocyanate while agitating at 30 to 35 C. The mixture is then heated at 77 to 80 C. for 4 hours and then cooled to room temperature. This prepolymer analyzes 6.35% -NCO groups.

100 parts of this prepolymer is then put into a vessel with an agitator and heated to 70 C. 19.5 parts of molten para,para'-methylene bis(ortho-chl0roaniline) at 120 C. is added. There is then immediately added 600 parts of crushed steel particles of 120 mesh size which are mixed in thoroughly. The mix is then poured within 2 minutes into a compression pad mold for a door panel and put in an oven at 50 C. for 2 days.

The polyurethane thus formed showed the following properties: I Tensile strength at the break, 25 C. :lb1/sq. in 1,500

Izod impact strength, 23.9 C. ft. lb../sq. iE \2 5 Compression set (Method A, 22 hrs. at. 70 C 1350 lb./sq. in.), percent 5 Compression deflection at 10% lb./sq. in 875 20% 1b./sq. in 1,875 30% lb./sq. in 3,000

EXAMPLE 4 Example 3 is repeated except that instead of the steel particles there is added 225 parts of granular aluminum particles having an average diameter of 33 mils. The volume ratio of metal to polyurethane is approximately the same. The product shows the following properties:

Tensile strength at the break, 25 C. lb./ sq. in 750 Izod impact strength, 23.9 C. 6.6 Compression set (Method A, 22 hrs. at 70 C. at

1350 lb./sq. in.), percent 7 Compression deflection at 10% lb./sq. in 1,275 20% lb./sq. in 2,800 30% lb./sq. in 4,125

EXAMPLE 5 To 5 00 parts of polytetramethyleneether glycol 1000 and 45 parts of 1,3-butanediol at 30 C., there is added 348 parts of a toluene diisocyanate containing of the toluene-2,4-diisocyanate and 20% toluene-2,6-diisocyanate. The mix is heated at 80 C. for 4 hours and cooled to room temperature. It shows 9.45% -NCO groups.

parts of this prepolymer is heated to 70 C. in a vessel provided with good agitation. To this is added 26 parts of molten para,para-methylene bis(ortho-chloroaniline) at C. There is immediately added 600 parts of crushed steel particles of 120 mesh size and the whole is mixed thoroughly. The mix is very promptly poured into a door panel flange pad mold and held at 50 C. for 50 hours. The product shows the following properties:

Tensile strength at the break lb./ sq. in 3,000

EXAMPLE 6 50 parts of prepolymer as prepared in Example 1 and 50 parts of the prepolymer as prepared in Example 3 were used. The mixture is heated to 70 C. in a vessel fitted with eflicient agitation and 23 parts of molten para,- para'-methylene bis(ortho-chloroaniline) is added at 120 C. After 30 seconds stirring, there is added 600 parts of crushed steel particles of 120 mesh size and stirring is continued for an additional minute. The mix is then cast into a mold for a compression pad for a curved panel. The mold is then cured for 50 hours at 50 C. The product has the following properties:

Tensile strength at the break lb./sq. in 875 Izod impact strength, notched ft. lb./sq. in 2.3 Compression set (Method A, 22 hrs., at 70 C., 1350 30% lb./sq. in 4,560

While the compression pad made of polyurethane compositions such as the foregoing has been shown in the preferred upper die member position and female in form, other arrangements are possible which in view of the present teaching Will be obvious to persons of ordinary skill in the art. In addition it is contemplated and within the scope of the present invention that certain applications might require the use of a metal backing and metal inserts with elastomer compression pads hereinbefore described.

As many apparently widely different embodiments of this invention may be made without departing from the spirit and scope thereof, it is to be understood that this invention is not limited to the specific embodiments thereof except as defined in the appended claims.

What is claimed is:

1. As an article of manufacture, a compression pad for use in a die adapted to position a shaped metal part for additonal Working operations, said compression pad having its face formed complementary to a surface of said shaped metal part and being composed of a polymeric composition selected from the .group consisting of cured polyalkyleneether polyurethane and cured polyalkyleneether polyurethane filled with metal particles, said cured polyalkyleneether polyurethane having a modulus at 100% elongation of 1500 to 4500 lb./sq. in., elongation at the break of 200 to 500%, a Shore D hardness of 45 to 80, and an Izod notch impact minimum of 10 foot lbt/in. of notch.

2. As an article of manufacture, a compression pad for use in a die adapted to position a shaped metal part for additional working operaitons, said compression pad hav- 8 prepolymer by reacting about one molar proportion of polytetramethylethyleneether glycol having a molecular weight of about 1000 and 0 to 1 molar proportion of 1,3- butanediol with 2 to 4 molar proportions of toluene diisocyanate, with the proviso that the ratio of NCO groups to the sum of the OH groups of the glycol and the diol is about 2, and (2) reacting said prepolymer with 85-99% by wt. of theory of para-para'-methylene bis(ortho-chloroaniline), said elastomeric polymer having a modulus at 100% elongation of 1500 to 4500 lb./sq. in., elongation at the break of 200 to 500%, a Shore D hardness of 45 to 80, and an Izod notch impact minimum of 10 foot lb./in. of notch.

33. A die arrangement in which a die member and a compression pad are adapted to position a shaped metal part for additional working operations, the improvement comprising having the compression pad being composed of a polymer selected from the group consisting of cured polytetramethyleneether polyurethane and cured polytetramethyleneether polyurethane filled with metal particles, said polytetramethyleneether polyurethane having a modulus at 100% elongation of 1500 to 4500 lbt/sq. in., elongation at the break of 200 to 500%, a Shore D hardness of 45 to 80, and an Izod notch impact minimum of 10 foot lb./in. of notch.

References Cited by the Examiner UNITED STATES PATENTS 2,133,445 10/1938 Guerin 11344 2,735,390 2/1956 Engel 11344 2,737,138 3/1956 Derbyshjre 11344 CHARLES W. LANHAM, Primary Examiner. 

1. AS AN ARTICLE OF MANUFACTURE, A COMPRESSION PAD FOR USE IN A DIE ADAPTED TO POSITION A SHAPED METAL PART FOR ADDITIONAL WORKING OPERATIONS, SAID COMPRESSION PAD HAVING ITS FACE FORMED COMPLEMENTARY TO A SURFACE OF SAID SHAPED METAL PART AND BEING COMPOSED OF A POLYMERIC COMPOSITION SELECTED FROM THE GROUP CONSISTING OF CURED POLYALKYLENEETHER POLYURETHANE AND CURED POLYALKYLENEETHER POLYURETHANE FILLED WITH METAL PARTICLES, SAID CURED POLYALKYLENEETHER POLYURETHANE HAVING A MODULUS AT 100% ELONGATION OF 1500 TO 4500 LB./SP. IN., ELONGATION AT THE BEAK OF 200 TO 500%, A SHORE D HARDNESS OF 45 TO 80, AND AN IZOD NOTCH IMPACT MINIMUM OF 10 FOOT LB./IN. OF NOTCH. 